Method for coupling light into a thin planar waveguide

ABSTRACT

A light distributing device ( 100 ) comprises a thin planar waveguide ( 10 ) and a waveguiding ridge ( 20 ). An incoming light beam (B 1 ) coupled into the ridge ( 20 ) forms a second light beam (B 2 ) waveguided in the ridge ( 20 ). The ridge ( 20 ) and the planar waveguide ( 10 ) have a common portion ( 23 ) such that light is further coupled from the side of the ridge ( 20 ) into the planar waveguide ( 10 ) through said common portion ( 23 ). Thus, optical power of a broad incoming beam (B 1 ) may be effectively coupled to a relatively thin planar waveguide ( 10 ). The planar waveguide ( 10 ) may further comprise diffractive out-coupling elements ( 30 ) to direct light towards a display ( 400 ).

RELATED APPLICATION

This application was originally filed as and claims priority to PCTApplication No. PCT/FI2006/050476 which was filed on Nov. 2, 2006.

FIELD OF THE INVENTION

The present invention relates to coupling light into planar waveguides.

BACKGROUND OF THE INVENTION

Planar waveguides are cost-effective devices to provide lighting fore.g. liquid crystal displays or keysets. Light which is initiallyprovided e.g. by an external light emitting diode (LED) may bedistributed to a larger area by means of a planar waveguide. The use ofthin planar waveguides may facilitate reducing size, weight andmanufacturing costs of a portable device.

Referring to FIG. 1, optical power may be lost when a broad light beamB1 emitted by a light source 200 impinges on the edge of a thin planarwaveguide 10, as the beam B1 overlaps only partially with the edge.

Referring to FIG. 2, optical power may be also lost when the lightsource is misaligned with respect to the edge of a thin planar waveguide10. The coupling efficiency may be degraded due to misalignment also ina case when the vertical dimension of the light beam is equal to orsmaller than the thickness of the planar waveguide. As the thickness ofthe planar waveguide may be e.g. 0.2 mm, and the manufacturingtolerances may be e.g. 0.5 mm, the alignment problem may be significantin mass production.

The arrangements of FIGS. 1 and 2 are herein called “directly edgecoupled” arrangements.

FIG. 3 of a patent publication US2005/0259939 discloses a furtherdirectly edge coupled arrangement wherein a planar waveguide has atapered edge portion to facilitate coupling of light into the planarwaveguide.

SUMMARY OF THE INVENTION

The object of the invention is to provide a device and a method forcoupling light emitted by a light source into a planar waveguide. Afurther object of the invention is to provide lighting for a display. Afurther object of the invention is also to provide lighting for akeyset.

According to a first aspect of the invention, there is provided a devicecomprising:

-   -   a ridge, and    -   a substantially planar waveguide comprising at least one        out-coupling portion, wherein said ridge has an end for coupling        light into said ridge in order to form a light beam waveguided        longitudinally within said ridge, said ridge and said planar        waveguide having a common portion to couple light out of said        ridge sideways into said planar waveguide, and said out-coupling        portion being adapted to couple light out of the plane of said        planar waveguide.

According to a second aspect of the invention, there is provided amethod of distributing light by using a ridge and a substantially planarwaveguide, said method comprising:

-   -   coupling light into said ridge to form a light beam waveguided        longitudinally in said ridge, and    -   coupling light out of said ridge sideways into said planar        waveguide through a common portion of said ridge and said planar        waveguide.

The light distributing device comprises a substantially planar waveguideand a waveguiding ridge. A light beam emitted by a light source iscoupled into the end of the ridge to form a second light beam which iswaveguided longitudinally in the ridge. The side of the ridge overlapswith the planar waveguide such that the ridge and the planar waveguidehave a common portion. Light is coupled sideways from the ridge into theplanar waveguide through said common portion. In other words, the lightconfined in the waveguiding ridge leaks in a transverse manner throughthe overlapping portion to the planar waveguide.

The height of the ridge is greater than the thickness of the planarwaveguide.

In an embodiment, a good efficiency of coupling the optical power of alight beam into a thin planar waveguide may be attained, although thethickness of the planar waveguide may be substantially smaller than thevertical dimension of the in-coupled light beam. The coupling efficiencymay be improved especially when compared with the directly edge coupledarrangement of FIG. 1.

In an embodiment, the ridge of the light distributing device facilitatesalignment of the light source when the vertical dimension of thein-coupled light beam is smaller than the height of the ridge. Thus,sensitivity to manufacturing tolerances may be reduced especially whencompared with the directly edge coupled arrangement of FIG. 2.

In an embodiment, the ridge of the light distributing device mayfacilitate providing a more uniform distribution of optical intensityinside the planar waveguide than what can be attained by the directlyedge-coupled arrangements, when using the same number of light sources.

In an embodiment, a relatively uniform distribution of light may beprovided by using only one light source.

In an embodiment, the improvement in the coupling efficiency, toleranceto misalignment, and a more uniform distribution of intensity in theplanar waveguide may be attained simultaneously.

In an embodiment, a thin keypad and/or a thin display may beimplemented.

The embodiments of the invention and their benefits will become moreapparent to a person skilled in the art through the description andexamples given herein below, and also through the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following examples, the embodiments of the invention will bedescribed in more detail with reference to the appended drawings inwhich

FIG. 1 shows a side view of prior art coupling of a broad light beaminto a planar waveguide,

FIG. 2 shows a side view of misalignment of a light source with respectto a planar waveguide,

FIG. 3 is a three-dimensional view of a light distributing devicecomprising a planar waveguide and a ridge for coupling light into saidplanar waveguide,

FIG. 4 shows an end view of a device according to FIG. 3,

FIG. 5 shows a top view of a device according to FIG. 3,

FIG. 6 shows, in an end view, dimensions of an illuminating light beamwith respect to the end of the ridge,

FIG. 7 a shows, in an end view, alternative positioning of anilluminating light beam with respect to the end of the ridge,

FIG. 7 b shows, in an end view, alternative positioning of anilluminating light beam with respect to the end of the ridge,

FIG. 8 a is a three-dimensional view of light distributing device,wherein a common portion between a ridge and a planar waveguide has beenindicated by a hatch pattern,

FIG. 8 b shows, in a three dimensional view, dimensions of the deviceaccording to FIG. 8 a,

FIG. 8 c shows a side view of the device according to FIG. 8 a,

FIG. 8 d shows a top view of the device according to FIG. 8 a,

FIG. 9 a shows the ratio of the optical power remaining in the ridge tothe optical power coupled into the ridge, as a function of the distancefrom the end of the common portion,

FIG. 9 b shows the ratio of the optical power coupled into the planarwaveguide to the optical power coupled into the ridge, as a function ofthe distance from the end of the common portion,

FIG. 10 a shows a three dimensional view of a light distributing devicecomprising a bifurcated tapered ridge waveguide,

FIG. 10 b shows a plot of light rays coupled into the planar waveguideaccording to FIG. 10 a,

FIG. 10 c is a comparative example showing a plot of light rays coupledinto a corner of a planar waveguide plate without using a ridge,

FIG. 11 shows, in a top view, a light distributing device comprising abent ridge,

FIG. 12 shows, in a top view, a light distributing device comprising aridge which is shorter than the planar waveguide,

FIG. 13 shows, in a top view, a light distributing device comprising aridge which is located on the edge of the light distributing device,

FIG. 14 shows, in a top view, various elements for re-directing lightwhich propagates in the planar waveguide,

FIG. 15 shows, in an end view, a ridge having a substantiallyrectangular cross section,

FIG. 16 shows, in an end view, a ridge having a rounded cross section,

FIG. 17 shows, in an end view, a light distributing device comprising aplurality of ridges,

FIG. 18 shows, in an end view, a ridge protruding from the upper and thelower side of the light distributing device,

FIG. 19 shows, in an end view, a ridge located on the edge of the lightdistributing device,

FIG. 20 shows, in an end view, a ridge attached to a planar waveguide,

FIG. 21 is a three-dimensional view of a portable device comprisinglight distributing devices to illuminate a keypad and a display,

FIG. 22 a shows an end view of a light distributing device comprising anopening to locally prevent coupling of light from the ridge into theplanar waveguide,

FIG. 22 b shows top view of a light distributing device according toFIG. 22 a,

FIG. 23 a shows, in an end view, depressions to locally reduce couplingof light from the ridge into the planar waveguide,

FIG. 23 b shows, in an end view, a plurality of dimensions associatedwith FIG. 23 a,

FIG. 24 shows, in a top view, the directions between light rays and thelongitudinal direction of the ridge,

FIG. 25 a shows, in a top view, a light distributing device comprisinglight redistributing features on the ridge,

FIG. 25 b shows, in a top view, a light distributing device comprising acurved ridge,

FIG. 25 c shows, in a top view, a light distributing device comprising atapered ridge,

FIG. 26 shows, in a top view, a light distributing device comprising tworidges to provide different propagation directions of light inside theplanar waveguide,

FIG. 27 shows, in a top view, coupling of light into the opposite endsof the ridge in order to provide different propagation directions oflight inside the planar waveguide, and

FIG. 28 shows, in an end view, the direction of a beam provided by anout-coupling element.

DETAILED DESCRIPTION

FIG. 3 shows a light distributing device 100 comprising planarwaveguides 10 a, 10 b, and a ridge 20 to couple light into the planarwaveguides 10 a, 10 b. A light beam B1 provided by a light source 200 iscoupled into an end 22 of the ridge 20 in order to form a light beam B2which propagates in the longitudinal direction SX of ridge 20.

The lower sides of the ridge 20 are optically coupled to the planarwaveguides 10 a, 10 b. Thus, a fraction of the light B2 propagating inthe ridge 20 is transversely coupled from the sides of the ridge 20 intothe planar waveguides 10 a, 10 b, in order to form light B3 whichpropagates in the planar waveguides 10 a, 10 b.

The light is confined to the ridge 20 and to the planar waveguides 10 a,10 b by total internal reflections, i.e. the light is waveguided in theridge 20 and the planar waveguides 10 a, 10 b.

The light distributing device 100 may further comprise one or moreout-coupling portions 30 to couple light out of the plane of the planarwaveguides 10 a, 10 b in order to form an out-coupled light beam B4. Theout-coupling portion 30 may be e.g. a diffraction grating. Theout-coupled light beam B4 may be viewed e.g. by a human viewer (notshown).

The incoming beam B1 may be provided by a light source which may be e.g.a light emitting diode (LED), a resonant cavity LED, or a laser. Thelight source 200 may be in contact with the end 22 of the ridge or atsome distance from it.

The horizontal direction SY is perpendicular to the longitudinaldirection SX of ridge 20, and the vertical direction SZ is perpendicularto the directions SX and SY.

FIG. 4 shows an end view of the light distributing device 100 accordingto FIG. 3. In-coupled light rays which fulfill the criterion for totalinternal reflection may be reflected once or many times on the walls ofthe ridge 20, and contribute to the light beam B2 propagating in theridge 20. When the light rays of the beam B2 impinge on the lower sideof the ridge, they may be coupled into the planar waveguides 10 a, 10 b,subsequently forming light beams B3.

FIG. 5 shows a top view of the light distributing device 100 accordingto FIG. 3. The rays of the incoming light beam B1 may be refracted atthe end 22 of the ridge 20. In-coupled light rays fulfilling thecriterion for total internal reflection constitute the light beam B2propagating in the ridge 20. A fraction of the light rays is coupledinto the planar waveguides 10 a, 10 b to form the light B3.

FIG. 6 shows the dimensions of the incoming light beam B1 with respectto the dimensions of the ridge 20. The incoming beam B1 has a height h9and a width w9. The end 22 of the ridge 20 has a height h2 and a widthw2. In order to minimize coupling losses, the width w2 may be greaterthan or equal to the width of the beam B1 and the height h2 may begreater than or equal to the height h9. The thickness h1 of the planarwaveguide 10 a may be smaller than the height h9 of the incoming beamB1.

w9 and h9 refer to the dimensions of the incoming beam B1 at the end 22of the ridge 20. The dimensions of the incoming light beam B1 may bedefined e.g. by an elliptical perimeter which encloses 70% of theoptical output power of a light source 200, and which perimeter enclosesthe minimum area.

FIGS. 7 a and 7 b show how the tolerance to the misalignment of theincoming light beam B1 may be substantially increased, thanks to theridge 20 of the light distributing device 100, when the width w2 of theridge is greater than the width of the beam B1 and when the height h2 ofthe ridge 20 is greater than the height of the beam B1.

Referring to FIG. 8 a, the light distributing device 100 may comprise asubstantially planar waveguide 10 and a ridge 20, wherein said ridge 20has an end 22 for coupling light B1 into said ridge 20 in order to forma light beam B2 waveguided in said ridge 20 in the longitudinaldirection SX of said ridge 20, and wherein said ridge 20 and said planarwaveguide 10 have a common portion 23 to couple light of said light beamB2 out of said ridge 20 into said planar waveguide 10 sideways withrespect to the longitudinal direction SX of said ridge 20.

The ridge 20 and the planar waveguide 10 overlap at least partially.

The longitudinal direction means the direction of the centerline 21 ofthe ridge 20. In case of a curved ridge 20 (FIGS. 11 and 25 b), thelongitudinal direction may locally deviate from the longitudinaldirection SX near the end 22 of the ridge 20.

The common portion 23 is defined to be at a location of minimum commoninterfacial area between the ridge 20 and the planar waveguide 10. Thecommon portion 23 is indicated in FIG. 8 a by a hatch pattern.

FIG. 8 b shows a plurality of dimensions associated with the lightdistributing device 100 according to FIG. 8 a. The ridge 20 has a lengthL2, and the planar waveguide 10 has a length L1. The common portion 23has a length L3 and a height h5. The length L3 of the common portion 23may be shorter than or equal to the length L2 of the ridge 20. Thelength L3 of the common portion 23 may be shorter than or equal to thelength L1 of the planar waveguide 10. The height h5 of the commonportion may be smaller than, greater than, or equal to the thickness h1of the planar waveguide 10 (see FIGS. 23 a, 23 b). The height h5 may bedifferent at different points CP of the common portion 23, i.e. atdifferent distances X from the end of the common portion 23. w1 denotesa width of the planar waveguide 10, as measured from the wall of theridge 20 to the edge of the planar waveguide 10.

The dimensions of a light distributing device 100 may be e.g. asfollows: The height h2 of the ridge 20 may be greater than or equal totwo times the thickness h1 of the planar waveguide 10. The width w2 ofthe ridge 20 may be greater than or equal to two times the thickness h1of the planar waveguide 10. The width w1 of the planar waveguide 10 maybe greater than or equal to ten times the thickness h1 of the planarwaveguide 10. The length L3 of the common portion 23 may be greater thanor equal to ten times the thickness h1 of the planar waveguide 10.

A significant improvement in the coupling efficiency may be gained eventhough the height h2 of the ridge 20 is only 1.5 to 2 times thethickness h1 of the planar waveguide 10.

The absolute thickness h1 of the planar waveguide may be e.g. in therange of 0.2 to 0.5 mm. In order to implement light and/or flexiblestructures, the thickness h1 may be in the range of 0.1 to 0.2 mm. Inorder to implement very light and/or flexible structures, the thicknessh1 may be in the range of 0.05 to 0.1 mm. In order to implementextremely light and/or flexible structures, the thickness h1 may besmaller than 0.05 mm. The lowest limit of the thickness h1 is defined bythe requirement to allow at least single mode waveguiding. The smallestthickness h1 may be e.g. 10 μm.

In order to implement e.g. light distributing device 100 to illuminate akeyset and/or display (FIG. 21), the width w1 and/or the length L1 ofthe planar waveguide may be e.g. in the range of 5 to 100 mm. If thedevice 100 comprises out-coupling portions 30, the sum of the areas ofthe out-coupling elements 30 may be e.g. greater than 5% of theone-sided area of the planar waveguide 10.

FIG. 8 c shows a side view of the light distributing device 100according to FIG. 8 a. FIG. 8 d shows a top view of the lightdistributing device 100 according to FIG. 8 a, when coupled to a lightsource 200.

In order to reduce the coupling losses, the height h9 of the beam B1emitted by the light source 200 may be smaller than or equal to theheight of the ridge 20. The width w9 of the beam B1 may be smaller thanor equal to the width of the ridge W2. The vertical divergence φ9 andthe horizontal divergence γ9 of the beam B1, the orientation of the beamB1 with respect to the end 22 of the ridge 20, and the index ofrefraction of the ridge 20 may be selected such that substantially alllight coupled into the ridge 20 fulfils the criterion of total internalreflection.

The beam B1 may be substantially collimated in the vertical and/orhorizontal directions. Thus, the vertical divergence φ9 and/or thehorizontal divergence γ9 may be smaller than 2 degrees. The beam B1 maybe diverging in the vertical and/or horizontal directions, i.e. thevertical divergence φ9 and/or the horizontal divergence γ9 may be in therange of 2 to 5 degrees, in the range or 5 to 20 degrees, or even in therange of 20 to 60 degrees. The beam B1 may be highly diverging, and thevertical divergence φ9 and/or the horizontal divergence γ9 may even bein the range of 60 to 180 degrees.

FIG. 9 a shows, by way of example, the ratio P₂/P₁ of optical power P₂propagating in the ridge 20 to the optical power P₁ initially coupledinto the end 22 of the ridge 20, as a function of the distance x fromthe end of the common portion 23. The ratio P₂/P₁ decreases with theincreasing distance x as more and more light has leaked from the ridge20 into the planar waveguide 10.

FIG. 9 b shows, corresponding to the situation of FIG. 9 a, the ratioP₃/P₁ of optical power P₃ coupled to the planar waveguide 10 to theoptical power P₁ initially coupled into the end of the ridge 20, as afunction of the distance x from the end of the common portion 23. Theratio P₃/P₁ increases with the increasing distance x as more and morelight has leaked from the ridge 20 into the planar waveguide 10.

The situation of FIGS. 9 a and 9 b corresponds to the following set ofparameters: Straight rectangular ridge 20 having a height of 0.4 mm anda width w2 of 1.0 mm. The ridge 20 has planar waveguides 10 a, 10 b onboth sides of the ridge 20, the thickness of the planar waveguides 10a,10 b and the height of the common portion 23 is 0.2 mm. The incominglight is provided by a LED which is located near the end 22 of the ridge20, The width W9 of the beam B1 is 1 mm and the height h9 of the beam B1is 0.4 mm. The divergence of the beam B2 propagating in the ridge 20 is39.2 degrees. The index of refraction of the ridge 20 and the planarwaveguides 10 a, 10 b is 1.58. The medium surrounding the ridge 20 andthe planar waveguides 10 a, 10 b is air having the refractive index ofone.

The coupling efficiency near the first end of the common portion 23,i.e. at low values of x may be increased e.g. by maximizing the ratio ofthe height h5 of the common portion to the height h2 of the ridge 20. Onthe other hand, a more uniform coupling efficiency at different valuesof x may be attained when the ratio of the height h5 of the commonportion to the height h2 of the ridge 20 is smaller.

The length L3 and the height h5 of the common portion 23 may be selectedfor example such that at least 20%, at least 50%, or even at least 90%of the optical power propagating in the ridge 20 can be coupled to theplanar waveguide 10.

FIG. 10 a shows a light distributing device 100 comprising a bifurcatedtapered ridge having branches 20 a, 20 b, and a single input end 22. Thearrangement of FIG. 10 a may be used for coupling light emitted from asingle light source 200 into a wide planar waveguide 10 in asubstantially uniform manner.

FIG. 10 b shows a plot of light rays coupled into the planar waveguide10 of FIG. 10 a. The light input end is at the upper left corner.

FIG. 10 c shows a plot of light rays coupled into the planar waveguideof FIG. 10 a, but without using the ridge. It can be noticed that thedistribution of light is substantially less uniform than in the case ofFIG. 10 b.

FIG. 11 shows a light distributing device 100 which has a bent ridge 20.The ridge 20 may have a curved portion 20 d to distribute light into awide area and/or to enhance coupling of light out of the ridge 20. Thecurved portion 20 d may couple a first portion 20 c of the ridge to asecond portion 20 e of the ridge 20. The curved portion 20 c and thesecond portion 20 e of the ridge may be used e.g. to reduce a differencebetween the intensities provided by a first out-coupling element 30 aand a second out-coupling element 30 b, especially when the firstout-coupling element 30 a is located between the first portion 20 c ofthe ridge and the second out-coupling element 30 b.

FIG. 12 shows a light distributing device 100 having a ridge which isshorter than the planar waveguide. The light distributing device 100 maycomprise a plurality of out-coupling elements 30 a, 30 b, 30 c.

FIG. 13 shows that the ridge 20 may also be at the edge of the lightdistributing device 100.

FIG. 14 shows various ways to re-direct and/or control light whichpropagates in the planar waveguide 10. For example, a diffractivegrating 56 may be used to change the direction of light. A reflectivesurface, e.g. an embedded mirror may be used to change the direction oflight. An opening 52 may be used block the propagation of light if theopening comprises light absorbing material or if the edges of theopening are cut such that light is diverted away from the plane of thewaveguide 10. The opening may also be adapted to act as a reflector, bytotal internal reflection.

FIG. 15 shows a ridge 20 having a substantially rectangular crosssection.

FIG. 16 shows a ridge 20 having a substantially rounded cross section.

A ridge 20 having a rectangular cross section may be used e.g. to keepthe horizontal divergence γ9 and the vertical divergence φ9substantially independent. For example, the use of the rectangular ridge20 may maintain the vertical divergence of the beam B2 below 2 degreesinside the ridge 20, although the horizontal divergence of the beam B2may simultaneously be as high as 30 degrees. In case of a rounded crosssection, a high horizontal divergence typically increases an initiallysmall vertical divergence.

FIG. 17 shows a light distributing device 100 comprising several ridges20 and several planar waveguides 10 a, 10 b, 10 c.

FIG. 18 shows a light distributing device 100 having a ridge whichprotrudes from the upper side and the lower side of the device 100.

FIG. 19 shows that an out-coupling portion 30 b, 30 c may direct lightout of the plane of the planar waveguide 10 such that an out-coupledlight beam B4 is transmitted through the planar waveguide 10. Anout-coupling portion 30 a, 30 d may also direct light out of the planeof the planar waveguide 10 such that an out-coupled light beam B4 is nottransmitted through the planar waveguide 10. The out-coupling portionsmay be on the upper or lower, i.e. on opposite sides of the planarwaveguide 10. The out-coupling portions 30 a, 30 b, 30 c, 30 d may bearranged such that the beams B4 emitted by them do not overlap, as shownin FIG. 19. The out-coupling portions 30 a, 30 b, 30 c, 30 d may also bearranged such that the beams B4 emitted by them overlap partially orcompletely.

FIG. 20 shows that the ridge 20 and the planar waveguide 10 may also beinitially separate components which are attached together by e.g. glueor welding. The one or more ridges 20 may be positioned on a planarwaveguide 10, as shown in FIG. 20. The one or two planar waveguides 10may also be butt-joined to the side or sides of the ridge 20.

One or more ridges 20 and one or more planar waveguides 10 may also beformed substantially simultaneously by e.g. embossing or moldingtechniques.

The ridge 20 and the planar waveguide 10 are of substantiallytransparent material, e.g. polycarbonate or acrylic. The index ofrefraction and the dimensions of the ridge 20 are selected to allowmultimode waveguiding. The planar waveguide may be substantially planarwaveguides, in other words, their upper and lower surfaces aresubstantially parallel and substantially planar. The planar waveguides10 may be perfectly planar or slightly bent, e.g. cylindrically orspherically bent. The planar waveguides 10 may be of stiff material orof flexible material.

The ridge 20 may be straight. The ridge 20 may also be curved, butlosses increase with the decrease of the curvature radius. The radius ofcurvature may be greater than 100 times the width of the ridge 20 inorder to keep the losses at a low level. The ridge 20 may be slightlytapered (FIG. 10 a) to increase the divergence of the beam B2 travellinginside the ridge 20 and/or to reduce the amount of transparent materialneeded to implement the ridge 20.

As the ridge 20 and the planar waveguide are waveguiding, their surfacesshould remain substantially smooth, clean and intact. The lightdistributing device 100 may be used such that it is protected from dirtand contamination. The ridge 20 and/or the waveguide 10 may be partiallyor completely covered with a protective layer having a lower refractiveindex than the ridge 20 and the planar waveguide 10.

One or more optical absorbers (not shown) may be attached to the planarwaveguide 10 and/or to the ridge 20 in order to prevent unwantedreflections.

The dimensions h1, W1, H2, W2, L1, L2 refer to the dimensions of thewaveguiding core of the ridge 20 and the planar waveguide 10, i.e., apossible cladding layer is not taken into consideration.

FIG. 21 shows a device 900 comprising a keyset 30 and/or a display 400.The keyset 30 may be a keypad or a keyboard. One or more lightdistributing devices 100 may be used to provide front and/or backlighting to e.g. a liquid crystal (LCD) display 400 or a MEMS display(Micro-Electro-Mechanical System). One or more light distributingdevices 100 may be used to provide lighting to a keyset 30.Touch-sensitive elements or switches 300 may be positioned under theback side of light distributing device 100, as shown in FIG. 21, if thedevice 100 is at least partially flexible. A set of proximity sensors300 may be positioned under the light distributing device 100.Alternatively, at least partially transparent touch-sensitive elements,switches and or proximity sensors may be positioned on the top of thelight distributing device 100 (not shown in FIG. 21).

The ridges 20 may also allow positioning of the relatively thick lightsources 200 to such that the outer dimensions of the device 900 may beoptimized and/or minimized. The ridges 20 may be positioned with respectto the other components of the device 900 such that the outer dimensionsof the device 900 may be optimized and/or minimized.

The device 900 may further comprise a battery, data processing and/ortelecommunications module 600. The device 900 may be portable. Thedevice 900 may comprise telecommunications capabilities. The device 900may be e.g. a mobile phone, and/or a computer.

Yet, the device 900 may be a personal digital assistant (PDA), acommunicator, a navigation instrument, a digital camera, a videorecording/playback device, an electronic wallet, an electronic ticket,an audio recording/playback device, a game device, a measuringinstrument, and/or a controller for a machine.

Referring to FIGS. 22 a and 22 b, the light distributing device 100 maycomprise one or more openings 52 to locally prevent coupling of lightfrom the ridge 22 to a portion 54 of the planar waveguide 10 a. Theridge side wall of the opening 52 may be located to the side of theridge and arranged to reflect light back into the ridge 20 by totalinternal reflection. The width w6 of the opening 52 may be greater thanthe wavelength of the light, e.g. greater than or equal to 1 μm. Tofacilitate manufacturing, the width w6 of the opening 52 may be greaterthan or equal to the thickness h1 of the planar waveguide 10 a. Theopening 52 may be implemented e.g. by die-cutting.

Referring to FIGS. 23 a and 23 b, the light distributing device 100 maycomprise one or more depressions 50 a, 50 b to locally reduce couplingof light from the ridge to the planar waveguide 10 a, 10 b. To the firstapproximation, the optical power coupled through the depression 50 a, 50b per unit length of the ridge 20 is proportional to the height h5 ofthe depression 50 a, 50 b. The height h5 may be selected to be differentat different distances x from the end of the common portion 23 (FIG. 8b). The height h5 may be smaller than or equal to the thickness h1 ofthe planar waveguide 10 a. The height h5 may be e.g. greater than orequal to 0.1 times the thickness h1 of the planar waveguide 10 a. Thewidth w5 of the depression 50 a, 50 b may be greater than the wavelengthof the light, e.g. greater than or equal to 1 μm. To facilitatemanufacturing, the width w6 of the depression 50 a, 50 b may be greaterthan or equal to the thickness h1 of the planar waveguide 10 a.

Referring to FIG. 24, the direction of the incoming light beam B1 may beat a non-zero horizontal angle γ8 with respect to the longitudinaldirection SX of the ridge 20 such that also the majority of the lightrays propagate at an non-zero angle β1 with respect to the longitudinaldirection inside the ridge 20, i.e. with respect to the centerline 21 ofthe ridge 20. The light rays coupled from the ridge 20 to the planarwaveguide 10 may be considered to constitute at least locally a lightbeam B3. The light beam B3 has a non-zero angle α1 with respect to thelongitudinal direction.

The light distributing device 100 may comprise one or more diffractiveout-coupling portions 30. An out-coupling portion 30 may havediffractive features which are at an angle γ1 with respect to thelongitudinal direction SX. The angle β1 and/or the angle γ1 may beselected to optimize the direction and/or the intensity of anout-coupled beam B4 diffracted by the portion 30 (FIG. 3). For example,the angle β1 and/or the angle γ1 may be selected to substantiallymaximize the intensity of the beam B4.

The local coupling efficiency near the first end of the common portion23 may be maximized by maximizing the angle γ8 of the incoming beam B1such that at least 70% of the light coupled through the end 22 of theridge 20 fulfills the criterion for total internal reflection. The localcoupling efficiency is herein defined to be the ratio of coupled opticalintensity in the planar waveguide to the intensity in the ridge, at adistance x from the end of the common portion 23.

On the other hand, a more uniform intensity distribution in the planarwaveguide 10 may be attained by selecting a small angle γ8 of theincoming beam B1.

In order to facilitate coupling between the ridge 20 and the waveguide10, the angle γ8 between the average direction of the beam B1 and thelongitudinal direction SX may be greater than three times arctan(w2/L3)and/or greater than three times arctan (h2/L3).

In order to facilitate coupling between the ridge 20 and the waveguide10, the horizontal divergence γ9 of the beam B1 may be greater thanthree times arctan(w2/L3) and/or vertical divergence φ9 of the beam B1may be greater than three times arctan (h2/L3).

In order to facilitate coupling between the ridge 20 and the waveguide10, the angle β1 between the average direction of the beam B2 and thelongitudinal direction may be greater than three times arctan(w2/L3)and/or greater than three times arctan (h2/L3).

In order to facilitate coupling between the ridge 20 and the waveguide10, the horizontal divergence of the beam B2 propagating in the ridge 20may be greater than three times arctan(w2/L3) and/or the verticaldivergence of the beam B2 propagating in the ridge 20 may be greaterthan three times arctan (h2/L3).

The end 22 of the ridge 20 may be substantially perpendicular to thelongitudinal direction SX. Alternatively, the end 22 may besubstantially inclined with respect to longitudinal direction SX inorder to change the direction of the beam B2 in the ridge 20. The end 22may be substantially planar. Alternatively, the end 22 may have a convexor a concave form to affect the divergence of the beam B2 coupled intothe ridge 20.

FIG. 25 a shows light redistributing features 40 a, 40 b adapted toenhance coupling of light from the ridge 20 into the planar waveguide10. One or more light redistributing features 40 a, 40 b may beimplemented on the walls of the ridge 20. The light redistributingfeatures 40 a, 40 b may be e.g. diffraction gratings and/or prismsadapted to direct the light of the beam B2 towards the common portion23.

In general, the light distributing features 40 a, 40 b may be adapted toincrease the angle β1 or angles between the light rays LR of the beam B2and the centerline 21 of the ridge 20. The increase of said angle β1enhances coupling of light from the ridge 20 into the planar waveguide10.

Also the walls of the ridge 20 may be inclined such that coupling oflight from the ridge 20 to the planar waveguide 10 is enhanced.

Light may be coupled from the ridge 20 to the waveguide 10 if theincoming beam has a substantial divergence φ9, γ9, if the angle β1 issubstantially different from zero, and/or if the ridge 20 compriseslight redistributing features 40 a, 40 b.

The light redistributing feature 40 a or 40 b may also be a curvedportion of the ridge 20. Referring to FIG. 25 b, the ridge 20 maycomprise one or more curved portions 20 d to increase an angle betweenlight rays LR waveguided inside the ridge 20 and the centerline 21 ofthe ridge 20. Thus, the curved portion 20 d enhances coupling of lightout of the ridge 20 into the planar waveguide 10. The centerline 21 isdrawn only partially in FIG. 25 b to preserve the clarity of the FIG. 25b.

The light redistributing feature 40 a or 40 b may also be a taperedportion of the ridge 20. Referring to FIG. 25 c, the ridge 20 may have atapered portion 20 f to increase an angle between light rays waveguidedinside the ridge 20 and the centerline 21 of the ridge 20. Thus, thetapered portion 20 f enhances coupling of light out of the ridge 20 intothe planar waveguide 10. In particular, the tapered portion 20 f mayincrease the divergence of the beam B2 propagating in the ridge 20. Thetapered portion 20 f may be vertically, horizontally and/or conicallytapered. The whole ridge 20 may be tapered.

Referring to FIG. 26, the light distributing device 100 may comprise afirst ridge 20 a to provide a first beam B3 a propagating in the planarwaveguide, and a second ridge 20 b to provide a second beam B3 bpropagating in the planar waveguide such that the first and the secondbeams have different directions a1, a2 with respect to the longitudinaldirection SX of the first ridge 20 a. The light distributing device 100may comprise two or more separately controlled light sources 200 a, 200b. Light provided by a first light source 200 a, may be coupled to thefirst ridge 20 a, and light provided by a second light source 200 b, maybe coupled to the second ridge 20 b.

The light distributing device 100 may further comprise at least twodiffractive out-coupling portions 30 a, 30 b. The direction of thediffractive features of a first portion 30 a may be defined by an angleγ1 l and the direction of the diffractive features of a second portion30 b may be defined by an angle γ2.

The angles α1, α2, γ1, γ2 may be selected such that light provided bythe first light source 200 a and coupled out by the first out-couplingportion 30 a has substantially greater intensity than light provided bythe first light source 200 a and coupled out by the second out-couplingportion 30 b. Respectively, light provided by the second light source200 b and coupled out by the second out-coupling portion 30 b may havesubstantially greater intensity than light provided by the second lightsource 200 b and coupled out by the first out-coupling portion 30 a.

Referring to FIG. 27, a first light source 200 a may be coupled to afirst end 22 a of a ridge 20, and a second light source 200 b may becoupled to a second end 22 b of a ridge 20 such that a first beam B3 aprovided by the first light source 200 a propagates in a firstdirectional and a second beam B3 b provided by a second light source 200b propagates in a second direction α2.

The light distributing device 100 may further comprise at least twodiffractive out-coupling portions 30 a, 30 b. The direction of thediffractive features of a first portion 30 a may be defined by an angleγ1 and the direction of the diffractive features of a second portion 30b may be defined by an angle γ2.

The angles α1, α2, γ1, γ2 may be selected such that light provided bythe first light source 200 a and coupled out by the first out-couplingportion 30 a has substantially greater intensity than light provided bythe first light source 200 a and coupled out by the second out-couplingportion 30 b. Respectively, light provided by the second light source200 b and coupled out by the second out-coupling portion 30 b may havesubstantially greater intensity than light provided by the second lightsource 200 b and coupled out by the first out-coupling portion 30 a.

The first 30 a and the second out-coupling portion 30 b may be adjacentto or near each other. The first 30 a and the second out-couplingportion 30 b may be divided into sub-portions, and the sub-portions ofthe first out-coupling portion 30 a may be interlaced with thesub-portions of the second out-coupling portion 30 b. The sub-portionsmay be e.g. pixels or stripes which together constitute a pattern or acharacter. The first 30 a and the second out-coupling portion 30 b mayalso be partially or completely overlapping.

Thus, for example, the device 900 of FIG. 21 may have at least two modesof operation. In a first mode light is coupled out by a first group ofout-coupling portions 30 a associated with a first visual appearance ofthe keyset (300), and in a second mode light is coupled out by a secondgroup of out-coupling portions 30 b associated with a second visualappearance of the keyset (300). The different visual appearances maye.g. correspond to a vertical and a horizontal orientation of a handhelddevice 900 with respect to a viewer.

The light distributing device 100 may be optimized to operate at apredetermined wavelength λ selected from the range of visiblewavelengths 400-760 nm. The light distributing device 100 may beoptimized to operate at the whole range of visible wavelengths 400-760nm.

The substantially planar surface of the planar waveguide 10, 10 a, 10 bmay have one or more out-coupling portions 30, 30 a, 30 b.

The out-coupling portion 30 and/or light redistributing features 40 a,40 b may be e.g. a diffractive grating, prism or mirror embossed, moldedor attached on, or embedded in the planar waveguide 10, 10 a, 10 b or inthe ridge 20. The out-coupling element 30 may also be a rough portion ofthe surface. The out-coupling element 30 may also be a substantiallytransparent object which is in contact with surface of the planarwaveguide 10 causing local frustration of total internal reflection.

The diffraction gratings of out-coupling portions 30 and/or lightredistributing features 40 a, 40 b may have a grating constant selectede.g. from the range of 0.4-4 μm.

Referring to FIG. 28, the planar waveguide 10 of the light-distributingdevice 100 may comprise one or more out-coupling elements 30 to couplelight out of the plane of the planar waveguide 10. An angle γ3 betweenaverage direction of the out-coupled beam B4 and the vertical directionSZ, may be in the range of 0 to 70 degrees, in particular in the rangeof 0 to 40 degrees. Respectively, an angle γ4 between the averagedirection of a beam B4 and the plane of the planar waveguide 10 may bein the range of 20 to 90 degrees, in particular in the range of 50 to 90degrees.

The light distributing device 100 may also be used e.g. to distributelight into a plurality of further waveguides, devices or opticalcomponents, which may be positioned near or in contact with the edges ofthe planar waveguide 10, in contact with the surface of the planarwaveguide 10, and/or near the out-coupling elements 30.

The light distributing device 100 may also be used to providelight-emitting signs. The signs may be e.g. extremely lightweight“fasten seatbelt” signs for airplanes, or luminous highway trafficsigns. In other words, a light-emitting sign may comprise a lightdistributing device 100, wherein the visual appearance of a lightemitting portion or portions may be defined by the perimeter of one ormore out-coupling elements 30, or by a mask superposed over one or moreout-coupling elements 30. The signs may have two or more light-emittingmodes and different visual appearances, as described above withreference to FIGS. 26 and 27.

For the person skilled in the art, it will be clear that modificationsand variations of the devices and method according to the presentinvention are perceivable. All drawings are schematic. The particularembodiments described above with reference to the accompanying drawingsare illustrative only and not meant to limit the scope of the invention,which is defined by the appended claims.

The invention claimed is:
 1. A device comprising: a ridge, asubstantially planar waveguide having a first surface and a secondsurface and comprising a plurality of out coupling portions on one of oron both of the first or second surfaces of the substantially planarwaveguide, wherein said ridge has an end for coupling light into saidridge in order to form a light beam waveguided longitudinally withinsaid ridge, said ridge and said substantially planar waveguide having acommon portion to couple light out of said ridge sideways into saidsubstantially planar waveguide, and said out-coupling portion beingadapted to couple light out of the substantially planar waveguide, thelight having substantially non-uniform intensity distribution on thefirst and second surfaces; and at least one of: a set of proximitysensors positioned under the substantially planar waveguide opposite theplanar surface, and at least partially transparent touch sensitiveelements positioned over the substantially planar waveguide adjacent tothe planar surface for providing in the device a keypad or a keyboard.2. The device according to claim 1, wherein at least one of saidout-coupling portions comprises a diffraction grating.
 3. The deviceaccording to claim 1, wherein said ridge comprises one or more lightredistributing features implemented on a wall of the ridge to enhancecoupling of the light from the ridge to the substantially planarwaveguide.
 4. The device according to claim 3, wherein each of the oneor more light redistributing features is implemented as a diffractiongrating or a prism.
 5. The device according to claim 1 furthercomprising a light source, wherein the end of said ridge is arranged tocouple light emitted from said light source into said ridge so as toform the light beam waveguided longitudinally within said ridge.
 6. Thedevice according to claim 5 further comprising a keyset, wherein said atleast out-coupling element is adapted to direct light out of the planeof said planar waveguide in order to form at least one light beamassociated with features of said keyset.
 7. The device according toclaim 5 further comprising a display, wherein said at least out-couplingelement is adapted to direct light out of the plane of said planarwaveguide in order to form at least one light beam adapted to providelight to said display.
 8. The device according to claim 1, in which theridge comprises a first ridge and the common portion comprises a firstcommon portion; the device further comprising: a second ridge having asecond common portion to couple light out of said second ridge sidewaysinto said substantially planar waveguide; in which the first and secondcommon portions are disposed along opposed sides of the substantiallyplanar waveguide.
 9. The device according to claim 1, in which thedevice comprises the at least partially transparent touch sensitiveelements.
 10. The device of claim 1, wherein at least two of theplurality of out coupling portions comprise diffraction gratings havinga different direction of diffraction features.
 11. The device of claim1, wherein at least one of the plurality of out coupling portions istransmitted through the substantially planar waveguide.
 12. The deviceof claim 1, wherein the light out of the substantially planar waveguidehave an average direction at an angle with a perpendicular to thesubstantially planar waveguide between zero and seventy degrees.
 13. Adevice comprising: a ridge having two or more bifurcated branches; and asubstantially planar waveguide comprising at least one out-couplingportion, wherein said ridge has an end for coupling light into saidridge in order to form a light beam waveguided longitudinally withinsaid ridge and the bifurcated branches, said ridge and said planarwaveguide having a common portion to couple light out of said ridge andthe bifurcated branches sideways into said planar waveguide, and saidout-coupling portion being adapted to couple light out of the plane ofsaid planar waveguide.
 14. A device comprising a light distributingmeans, said light distributing means comprising: a first waveguidingmeans having a first surface and a second surface and comprising aplurality of light out-coupling means on one of or on both of the firstor second surfaces of the first waveguiding means, and a secondwaveguiding means, wherein the second waveguiding means is thicker thansaid first waveguiding means, said second waveguiding means having alight receiving means to couple light into said second waveguiding meansto form a light beam waveguided longitudinally in said secondwaveguiding means, said first waveguiding means and said secondwaveguiding means having a common portion to couple light out of saidsecond waveguiding means sideways into said first waveguiding means, andsaid out-coupling means being adapted to couple light out of the firstwaveguiding means, the light having substantially non-uniform intensitydistribution on the first and second surfaces; the device furthercomprising at least one of a set of proximity sensors positioned underthe first waveguiding means opposite the planar surface, and at leastpartially transparent touch sensitive elements positioned over the firstwaveguiding means adjacent to the planar surface for providing in thedevice a keypad or a keyboard.
 15. The device according to claim 14further comprising a light source, wherein said light receiving means isarranged to couple light emitted from said light source into said secondwaveguiding means.
 16. The device according to claim 14, in which thesecond waveguiding means comprises a first and a second ridge disposedalong opposed sides of the first waveguiding means.
 17. The deviceaccording to claim 14, in which the device comprises the at leastpartially transparent touch sensitive elements.
 18. The device of claim14, wherein at least two of the plurality of out-coupling means comprisediffraction gratings having a different direction of diffractionfeatures.
 19. The device of claim 14, wherein at least one of theplurality of out-coupling means is transmitted through the firstwaveguiding means.
 20. The device of claim 14, wherein the light out ofthe first waveguiding means have an average direction at an angle with aperpendicular to the first waveguiding means between zero and seventydegrees.